The present disclosure generally relates to a system and method for determining a flexible fuel ethanol concentration, and more particularly relates to a system and method for distinguishing a change in flexible fuel ethanol concentration from a hardware malfunction.
Flexible fuel vehicles are able to run on mixtures of gasoline and ethanol. As the properties of the flexible fuel may vary from one refueling to the next, engine control software of the flexible fuel vehicle needs to learn the properties of the flexible fuel in the vehicle so as to optimally control operation of a vehicle engine. One example of a potentially variable flexible fuel property relates to an ethanol concentration of the flexible fuel. Specifically, different flexible fuel sources may provide flexible fuel having different ethanol concentrations. Therefore, the vehicle engine control software preferably learns the ethanol concentration of flexible fuel in a vehicle fuel tank so as to accordingly control vehicle fuel injection.
To detect ethanol concentration of a flexible fuel, modern flexible fuel vehicles typically do not use ethanol sensors. Rather, modern flexible fuel vehicles rely on air-fuel sensors to provide air-fuel feedback, which is used to estimate the ethanol concentration of the flexible fuel in the vehicle fuel tank based on changes in a stoichiometric air-fuel ratio. However, air-fuel feedback offsets caused by changes in ethanol concentration may not be distinguishable from offsets caused by hardware variation or malfunction. In markets having on-board diagnostic regulatory requirements for fuel metering malfunctions, such as those set forth by the California Air Resources Board, this may pose both an operational and a regulatory problem.